I was doing some digging in to bottom brackets this weekend. I am trying to get a quad chain ring adapter to work.

What I have now is a 118mm square shaft bottom bracket. On the drive side I have 5mm of spacers so the crank is shifted over to the right (drive side) 5mm from stock. I still don't have enough room on the frame side for the derailleur to move in far enough to drop the chain on the 4th ring. I think I need another 4mm. I measured it just now and I think 3mm may get it, but it would be awfully tight.

This weekend I found some other bottom bracket sizes. Most of them top out at 127mm.

So here is where I am. If I take off the 5mm worth of bottom bracket spacers and put a 127mm bottom bracket on (9mm wider than what is on there now) that leaves me with 4.5mm, if it is centered, on each side that I am wider than stock - a bit narrower on the drive side than I am sitting now with the 5mm worth of spacers. If I add back in the spacers (all of them) I can get up to 4.5mm past where I am now - 5mm spacers on top of the extra 4.5mm space that the wider bottom bracket would give me. I am still shifting the whole crank over to the drive side 5mm past center, though = less thread engagement and off-center pedaling.

Thoughts? Are there any wider bottom brackets than 127mm that may be out there that I have not come across? If I could get up over 130mm (like a 133-134mm?) that may be a lot better for me.

IMO you'll be better served by maximizing the derailleur's inward swing and minimizing the amount of crankset outward shift. You might consider dremeling down the inner stop until the derailleur hits the frame. Some frames have dented seat tubes to further increase inward travel. Then lengthen the BB, or space it out only as much as needed.

The inward swing is as far as it will go. The derailleur bottoms out against the rear fender. I am not going to hack my fender up. If I had a thinner derailleur arm (area where the chain passes) that may be an option, but that would also cause an issue with the chain rubbing and would add to the difficulty in finding a position where the chain does not rub.

Get a lower profile crankset.
yours originally used a 118 spindle
find a crankset designed for a 110 or less
this will give you more room to work with considering 127 tends to be max

I have a quad and I think my spindle is 127mm and it was enough, but details depend on the frame. I also have a 132mm spindle (TA Specialites) in my stock, but in the end did not need to use it for the purpose. (My 127 is Ti and 132 is steel.) The ability to move the spindle off center was critical to get the innermost ring as close as possible to the frame but without any scratching.

I cut the fender and I filed down both stops in the original derailleur, as Ankelwork suggested. However, more recently I found out a better derailleur solution that did not require me to muck with the stops at all, in direct-mount derailleurs. They are used for carbon frames but also for fat bikes and you can get adapters for them. The triple ones have a more generous swing than the clamp-on derailleurs, possibly to make it easier to deal with variety of situations on fat bikes. With the adapters you can push them as far as you want away from the seattube. Getting them closer should be possible too, but would require mucking with the mounts. I even started that, but in the end just used the standard mount and it worked after some tweaking of the cage. My quad is fully indexed and works in practice like butter.

Has anyone seen the Bullseye and Phil Wood & Co. bottom brackets?

I'm looking at the Phil Wood's - they have a 135mm. Though, I will have to research them a bit more. I am not sure if that will work with my frame or not yet. The parts look a bit different.

I have an old loose ball one used in my similar quad crank experiment .. (want it?)

and you have not tapped into Phil Wood Co's range of BBs, as you just saw,
for tandem rear cross over drive there is need for a wider one..

I have one of those too .. I can trade it for a shorter one with you ( I can press the Spindle out
or trade it with you dor a shorter one that I can use when my 'unxx' 127.2* needs replacement)


Phil's Cartridge BB mount with 2 threaded Rings .. made in all sorts of threading types .. in California..

*Its what I have now to get A Rohloff Chain line..
got the phil in a trade with someone else.. so it Goes.

In San Jose, CA; only a few blocks for where I live, and a just a couple of blocks from the GordonBiersch brewery

Thanks for the additional info on the Phil Wood's fietsbob. I don't want to trade anything, I'd like to keep the bottom bracket I have.

I will look in to this more as I have time. I have a lot of ideas and projects right now - just not the time to do all of them.